Tunable high frequency circuits



March 21, 1944. J. a. SHERMAN TUNABLE HIGH FREQUENCY CIRCUIT Filed March 10, 1942 QMEERQU. WQQQRD U Q? Q wk P34 INVENTOR Jesse B. SHEFM/IN BY WQW ATTORNEY Patented Mar. 21, 1944 TUNABLEH men FREQUENCY omourrs Jesse B. Sherman, New York, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 10, 1942, Serial No. 434,027

'7. Claims.

MYPIIGSent invention relates. to parallel signal ran m ss n a ne u il z g, awmm n s g a collecting circuit.

In the past the superheterodyne type of radio receiving system has received preference in television reception. This was partly due to the fact that the. audio and video frequencies can readily be isolated by. rejection circuits of fixed tuning As is well known in television reception, the audio and video. bands occupy different portions of the assigned frequency range for a given station. The sound and video carriers are both positioned with: in the assigned range which may be some 6 megacycles wide. In general, there is the same prob: lem in the case of a common signal collector feeding separate signal transmission channels, wherein the transmission ranges are. relatively. close to each other.

Accordingly, it may be stated that it is one of the main objects of my invention to provide a television receiving system having a signal select ion input circuit fed by a common antenna circuit, the selective input circuit being of the tuned radio frequency type provided with means for automatically isolating the video carrier and audiocarrier frequencies.

Another important object of the invention is to provide parallel signal transmission systems which are tunable, and the transmission ranges being different; a common signal collecting cirquit-feeding both systems, the, signal amplifier systemsbeing provided with tuned circuits func: tioning as wave traps for the opposite amplifier frequencies, and, in addition, the amplifiers benew connected that voltage of one frequency range present between the antenna and ground will be degenerated in passing through the am pli fier of theother frequency range. Still other objects of my invention are to improve the tuner networks of television receivers, and more especially tov provide a tuner network of the tuned. radio frequency type which is economical to manufacture and assemble in radio re enera- Thenovel featureswhich I believe to be characteristic of. my invention are set forth in particularity in the appended claims; the invention itself, however, as toboth its organization and method of operation will best be understood by reference to. the following description taken in connection with the drawing in which I have. indicated diagrammatically a circuit organization wherebymy invention may be carried into efiect. Referring now to the accompanying. drawing,

there is shown only so much of the selection network'of a television receiver as is pertinent to the present invention. The numeral l indicates the signal collector element, which may be an antenna of the dipole. type, the usual type of antenna, or a radiofrequency distribution line. The antenna is connected to ground through a pair of coils 2 and 3 arranged in series. In shunt with coil 2 is arranged the variable tuning condenser 3, and in shunt with coil 3 is arranged a variable tuning condenser 4. The symbol Fv designates the fact that thecircuit 3-2 is tuned to the video carrier frequency. The symbol Fa designates the fact that circuit 4--3 is tujnedto the audio carrier frequency.

"As thoseskilled in the art of television reception well know, the video modulation frequencies are applied to a carrier whose frequency is located in the ultra short wave, spectrum. The audio frequencies modulate a carrier in the same range, but spaced by a predetermined high frequency from the video carrier. For example, in a given television station the picture carrier fre quency may be at, 51.25 mc. (megacycles), while the sound carrier frequency is at 55.75 mc. Both the video and audiocarriers are radiated. When using a superheterodyne type of receiver, the sig nal selector is adjusted to receive both carriers, and the latter are separated in separate intermediate frequency channels of the receiver after the converter.

According to the present system, however, the carrier frequencies are immediately separated in the antenna circuit. It is for this reason that the video carrier channel input circuit 32 is tuned to the frequency Fv, while the circuit 5-3 is tuned to the audio carrier frequency Fa. The video modulated carrier energy is amplified by an amplifier tube 5, which may be for example of the pentode type. The control grid 6 of the amplifier 5 is connected to the upper end of input coil 2, while the cathode I is connected to the lower end of coil 2 through the usual self-biasing resistor 3, the latter. being shunted by a carrier frequency by-pass condenser 9. The plate of amplifier 5 is connected to a source of-positive potential through coil 2. v

The latter is shunted by the variable tuning condenser 3'. Circuit 2'3 is tuned to the video carrier frequency Fv. The dotted line If! denotes the uni-control adjusting mechanism which varies the variable condensers 3 and 3' in unison. As is well known in the art, the rotors of condensers 3 and 3' would be mounted for common adjustment by mechanical adjusting shaft ll}.

The carrier voltage developed across 23 would be transmitted to additional stages of video carrier amplification by the coupling condenser II. The remainder of the video channel is well understood in the art, and is not necessary to a proper understanding of the presnt invention. Additional degeneration, as at the tube 5, could be had in the next stage or stages.

The audio modulated carrier channel comprises the radio frequency amplifier tube l2, which may also be of a pentode type. The cathode I3 is connected to ground through a selfbiasing resistor I4, the latter being shunted by the carrier by-pass condenser i 5. The signal input grid l6 of tube I2 is connected to the low potential end of resistor 8, and by lead l6 to the junction of coils 2 and 3. The plate of tube [2 is connected to a point of positive potential The adjustment of these variable condensers may be the same as in the case of variable con-. densers 3 and 3'. Of course, the variable con-. densers 3 and 3' would be tunable through the The audio line ill designates a second uni-- range of various video carrier frequencies, Whereas the condensers 4 and 4" would be tunable through the range of audio carrier frequencies, assuming the receiving system was to be tuned to different television stations. The coupling condenser ll transmits the audio modulated carrier voltage developed across tuned circuit 3 -4 to the remaining stages of the audio carrier channel. It will be seen that the two tuned antenna circuits act both to provide input energy for their respective amplifiers 5 and I2, and, additionally, provide wave traps for the opposite amplifier tubes. In other words, the tunable input circuit 32 functions as a wave trap for the audio carrier energy, while the tunable circuit 43 functions as a wave trap for the video modulated carrier energy. In addition, voltage of the audio carrier energy which exists between the collecting element I and ground will be degenerated in passing through the video amplifier tube 5.

This degenerative action occurs because the cathode circuit of the video carrier amplifier 5, considering the voltage applied between the antenna l and ground, is always resonant to the audio carrier frequency Fa. hi other words, the transmission of audio carrier energy to circuit 2'--3 is not only prevented by virtue of the wave trap action of circuit 4-3, but, in addition, the audio modulated carrier voltage applied to grid Swill develop across resonant circuit 43 audio carrier voltage which is in degenerative phase with respect to the audio carrier voltage which might exist initially at grid 6. Since circuit 43 is tuned to the audio carrier Fa, it represents a high impedance tothe audio carrier. Signal present between antenna and ground, applied to grid 6, will suffer high degeneration in its transmission through the video stage. Hence, it will be seen that circuit 4-3 performs a double function in that it acts as a wave trap for video carrier energy, and, also, acts to degenerate any audio carrier voltage which may exist at the grid 6 of the video amplifier 5. The response curve of the circuits 32 will, of course, be wide enough to Fv. The response'curveof circuits 4-3 will be wide enough to pass the modulation side bands of the carrier Fa.

While I have indicated and described one system for carrying my invention into efiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

l. A method of receiving modulated carrier energy of one frequency and modulated carrier energy of a different carrier frequency, which includes the steps of collecting both modulated carrier energies, selecting the modulated ener y of one carrier frequency, amplifying the selected carrier energy, selecting independently the modulated energy of the second carrier frequency, amplifying the second carrier ener y, and concurrently degenerating during said first selection step any modulated carrier voltage of said second carrier frequency which may exist durin said first selection step. I

2. In a selecting system for video modulated carrier energy and audio modulated carrier energy, a common antenna circuit including a pair of independent selector circuits arranged in series, a first amplifier tube having input electrodes coupled to one of said selector circuits, 2. second amplifier tube having input electrodes coupled to the second selector circuit, and the second selector circuit being arranged in the space current path of the first amplifier tube thereby to provide degeneration of modulated carrier voltage whose carrier frequency is to be selected by said second selector circuit. 3. In a system for receiving picture-modulated carrier energy and separate sound modulated carrier ener y, a common antenna circuit including a first circuit arranged to be tuned to said picture carrier frequency, an amplifier therefor having its input electrodes coupled to the said selector circuit, a, second selector circuit arranged to be tuned to the sound carrier frequency, a second amplifier having its input electrodes coupled to the second selector circuit, and said second selector circuit being. arranged in the space current path of said first amplifier tube whereby voltage of the picture carrier energy applied to the input electrodes of the first amplifier tube is degenerated by virtue of the inclusion of said second selector network in ,said space current path.

4. A method of receiving picture modulated carrier energy of one frequency and sound modulated carrier energy of a different carrier frequency, which includes the steps of collecting the combined modulated carrier energies, selecting the modulated energy of the picture carrier frequency, amplifying the selected energy, selecting independently the modulated energy of the sound carrier frequency, amplifying the sound carrier energy, and concurrently degenerating during said first selection step any modulated carrier voltage of said sound carrier frequency which may exist during said first selection step.

5. In a selecting system for video modulated carrier energy and audio modulated'carrier energy, a sole antenna circuit including a pair of independent selector circuits, an amplifier tube having input electrodes coupled to one of said selector circuits, and the second selector circuit being arranged in the space current 'pathof the first amplifier tube thereby to provide degeneration of modulated carrier voltage whose carrier frequency is to be selected by said second selector circuit. I

6. In a system for receiving picture-modulated carrier energy of the order of 50 megacycles and separate sound modulated carrier energy spaced therefrom by a frequency of the order of 6 megacycles, a single antenna circuit including a first selector circuit arranged to .be tuned to said picture carrier frequency, an amplifier therefor having its input electrodes coupled to the said selector circuit, a second selector circuit arranged to be tuned to the sound carrier frequency, said two selector circuits being in series, and said second selector circuit being arranged in the space current path of said amplifier tube whereby voltage of the picture carrier energy applied to the input electrodes of the amplifier tube is degenerated by virtue of the inclusion of said second selector network in said space current path.

7. In a system for receiving picture-modulated carrier energy and separate sound modulated carrier energy, a common antenna circuit including a first selector circuit arranged to be tuned to said picture carrier frequency, an amplifier therefor having its input electrodes coupled to the said selector circuit, a second selector circuit in series with the first selector circuit and arranged to be tuned to the sound carrier frequency, a second amplifier having its input electrodes coupled to the second selector circuit, and said second selector circuit being arranged in the space current path of said first amplifier tube whereby voltage of the picture carrier energy applied to the input electrodes of the first amplifier tube is degenerated by virtue of the inclusion of said second selector network in said space current path.

JESSE B. SHERMAN. 

